In order to warn the public of pending dangerous weather conditions, civil defense type situations, and the like, the Emergency Broadcast System (EBS) interrupts normal AM and FM station broadcasts and transmits a carrier heavily modulated by a tone having a constant frequency of one thousand (1000 ) Hertz. Following this warning tone which lasts for a period of fifteen seconds, a description of the emergency condition and instructions as to safety measures are given. This same procedure is adaptable to all bands including special service, such as weather and police. If an individual is to receive the warning, he must, of course, be listening to a radio, otherwise, he will not receive the emergency warning in the event one is broadcast.
Various alarms are currently used to warn an individual, during the time he is not listening to a radio, that an emergency broadcast is being transmitted. To my knowledge, these alarms are activated either by relying on the EBS practice of interrupting the station carrier wave prior to the warning signal transmission, or by providing filter circuitry to select the EBS signal having a frequency of 1,000 Hertz. Once the alarm is activated, a buzzer, bell, light or other device is relied on as an instruction to the individual to listen for the forthcoming EBS broadcast. Due to their complex circuitry, these alarms are expensive and generally adaptable only to a single type of radio.
The primary object of the present invention is to provide an alarm circuit, associated with a household radio, activated by the increased voltage of a sustained tone signal appearing as modulation on a carrier that is more heavily modulated than during normal station broadcasting, and operable to allow this signal to be broadcast over the speaker of the radio.
Another object of this invention is to provide an alarm circuit which is adaptable to any type of radio whether it be tube, transistorized with an audio output transformer, or transistorized with a direct transistor output, and which is operative with a radio having any type of voltage source, whether it be AC, DC, or a combination thereof.
Another object of this invention is to provide an alarm circuit having an open circuit when inoperative and in which, therefore, power consumption is minimized.
A further object of this invention is to provide an alarm device having simplified circuitry which can be economically manufactured and easily installed in radios.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.